1. Field of the Invention
The present invention relates to optical sensors, more specifically to multispectral target detection using optical sensors.
2. Brief Description of Related Art
One of the most common uses of optical sensors in a military setting is to detect and counter launched ordnance as part of a threat detection system. To achieve maximum protection of a host platform, it is crucial to rapidly detect a threat and accurately identify a type of the threat detected while minimizing use of processing resources. One way to achieve this end is by recognizing a spectral signature of a point source in an optical field of view (FOV).
Each type of launched ordnance typically emits a signature consistent radiant intensity in each spectral band and of consistent spectral ratio. Typically, detecting such signatures becomes more complex because the optical sensors often record many non-target, background sources of radiation, which can obscure a true threat signature. Thus, in order to properly identify a detected threat, these background sources of radiation must be understood, analyzed and accounted for.
Existing method for determining a spectral ratio of the image background is to find the average spectral ratio of a group of pixels surrounding an area of interest on a data capture (frame). However, this method is vulnerable to corruption if even just one or two pixels have aberrant radiant properties. The vulnerability in the existing method stems from the inability to account for the true background sources. Rather, the ratio and average intensity can be easily influenced by other phenomenon, because they are merely based on an average of arbitrary group of pixels.
Further, sensor conditions also create a spectral bias offset. Under the existing method, an attempt is made to eliminate this spectral bias offset by applying a median filter to the intensity value for each spectrum before applying an average-based spectral background ratio and subtracting intensity values from each spectrum. Unfortunately, this method requires substantial processing power to apply the filter to each spectrum and this separated filtering may introduce noise into the image because the background source has not yet been removed.